System and method for controlling the switching on of ancillary equipment driven by an engine

ABSTRACT

A method and system for controlling the switching in of ancillary equipment driven by an engine of a vehicle, the ancillary equipment being arranged to be driven by the engine until at least a minimum operating level relating to the status of the ancillary equipment is attained. The method includes the steps of: determining in which of three modes the vehicle is in, these modes being a first mode in which the engine is driving the vehicle, a second mode in which the vehicle is being braked and a third mode in which the vehicle is coasting; and in the first mode causing the ancillary equipment to be switched in only if the status of the ancillary equipment is below a predetermined minimum level; in the second mode causing the ancillary equipment to be switched in if the status of the ancillary equipment is below a predetermined maximum level; and in the third mode causing the ancillary equipment to be switched in only if the status of the ancillary equipment is below a predetermined intermediate level between the maximum level and the minimum level.

TECHNICAL FIELD

The present invention relates to a system and a method for controllingthe switching in of ancillary equipment driven by an engine of avehicle, said ancillary equipment being arranged to be driven by saidengine until at least a minimum operating level relating to the statusof said ancillary equipment is attained.

BACKGROUND OF THE INVENTION

It is a general goal within the vehicle industry to reduce fuelconsumption of vehicles, both to save natural resources and to reduceexhaust emissions. The fuel consumption of a motor vehicle can bereduced not only by optimizing the efficiency of the vehicle's engine,but also by e.g. reducing the weight of the vehicle and its aerodynamicdrag. Even once the design of an engine and the vehicle to which it isbeen fitted has been established, it is still possible to affect theactual fuel consumption of the vehicle by ensuring that the engine isplaced under load only when absolutely necessary.

In this respect, it is to be observed that the engine of a vehicle isemployed not only to propel the vehicle, but also to drive ancillaryequipment such as pumps and electrical generators. A typical example ofa piece of ancillary equipment for a commercial vehicle is an aircompressor for charging an air tank used to power the vehicle's brakingsystem. Upon starting the engine of a vehicle equipped with such abraking system, the air compressor is driven by the engine until atleast a minimum operating value of air pressure is attained in the airtank. Thereafter, the air pressure in the tank is maintained betweenpredetermined maximum and minimum values by recharging the tank eachtime the air pressure drops below the minimum value. Naturally, eachtime the air compressor is switched in, a load is placed on the engine.

It is known from e.g. EP-A-0 335 086 to provide a system which detectswhen a vehicle engine is not being used to propel the vehicle and toallow ancillary equipment to be switched on under such a condition.Thus, in said document, a sensor detects when the throttle pedal isreleased, thereby indicating that no additional propulsive force ispresently required by the driver, and thereafter allows ancillaryequipment to be switched on should activation of the equipment benecessary. For example, if the air pressure in the air tank is at a lowlevel, once the throttle is released, the air compressor is switched on.Since the engine is not being used to propel the vehicle, it will be thekinetic energy of the vehicle which drives the air compressor. As such,the engine requires no additional fuel to compensate for the load placedon the engine by the air compressor.

Although the system described above makes use of the kinetic energy ofthe vehicle to power items of ancillary equipment, the switching on ofthe ancillary equipment will increase the engine braking effect of theengine on the vehicle. As a consequence, a condition may arise in whichthe driver of the vehicle, when anticipating the need to reduce thespeed of the vehicle somewhat due to the fact that e.g. the vehicle isapproaching a corner, lifts his foot from the throttle to allow thevehicle to coast under normal engine braking. If, however, the liftingof his foot from the throttle pedal should result in a piece ofancillary equipment switching on, then the degree of engine braking willbe greater than that anticipated by the driver. As a consequence, thedriver may well need to reapply the throttle to ensure that the vehiclereaches the corner at the originally intended speed.

Since every application of the throttle implies an increase in theconsumption of fuel, it would be desirable to provide a system whichcould ensure that increased engine braking due to the switching on ofancillary equipment occurs only when it is desirable to significantlyreduce the kinetic energy of the vehicle.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a systemby means of which the kinetic energy of a vehicle can be conserved to ashigh an extent as possible by carefully controlling when switching on ofancillary equipment takes place.

This object is achieved by the system according to claim 1.

In accordance with the present invention, by distinguishing between“active” braking, i.e. activation of a vehicle braking system, andmerely coasting of the vehicle, the system can ensure that, withincertain safety constraints, ancillary equipment is switched on only whenthe vehicle is being actively braked.

It is a further object of the present invention to provide a method foroptimising the timing of the switching on of ancillary equipment drivenby an engine of a vehicle.

This object is achieved by the method according to claim 4.

Advantageous embodiments of the invention are detailed in the respectivedependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in the following in greater detail byway of example only and with reference to the attached drawings, inwhich

FIG. 1 is a schematic representation of various pressure levels in apiece of ancillary equipment;

FIG. 2 is a block diagram of one embodiment of the system according tothe present invention, and

FIG. 3 is a schematic representation of various temperature levels in apiece of ancillary equipment.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS:

Although the present invention may be practiced on any motor vehiclewhich is provided with ancillary equipment driven by the vehicle'sengine, the invention will be described in the following when applied toa heavy goods vehicle (HGV).

An HGV is normally propelled by a diesel engine. The engine is furtherused to drive ancillary equipment. Within the context of the presentinvention, the term “ancillary equipment” covers any system on thevehicle which requires intermittent charging or input from the engine. Anon-exhaustive list of examples of such systems includes a primarybraking system which utilizes a source of compressed air generated by anair compressor driven by the vehicle's engine, a cooling fan forassisting in the cooling of the engine, a servo system for the steeringsystem of the vehicle, an alternator for charging batteries in thevehicle, and a compressor for an air-conditioning unit. For the sake ofclarity, the present invention will be described in the following withrespect to the air supply for the braking system of a HGV.

With reference to FIG. 1, the braking system of an HGV is designed tooperate between a maximum pressure P_(max) and a minimum pressureP_(min) of compressed air. The compressed air is stored in an air tankand the tank is charged by an air compressor driven by the engine of thevehicle. Typical values for P_(max) and P_(min) are 12 bar and 8 barrespectively.

In FIG. 2, reference numeral 10 generally denotes a system according tothe present invention for controlling the switching in of the aircompressor. The system comprises a central processing unit (CPU) 12which collects data relating to various operating parameters of thevehicle. These parameters include the speed of the vehicle, the enginespeed, the amount of fuel delivered to the engine and the intakemanifold pressure. Parameters relating to the status of ancillaryequipment are also delivered to the CPU 12. In the present embodiment,this parameter is the prevailing pressure in the air tank.

The system 12 further comprises means for determining whether the engineis driving the vehicle, whether the vehicle is being braked or whetherthe vehicle is merely coasting. In this respect, the term “coasting”means that the driver of the vehicle is neither applying any pressure onthe throttle pedal nor applying any brakes. Accordingly, the term“braked” implies that the driver of the vehicle is applying some form ofbraking over and above normal engine braking. Such a form of brakingcould be via the foot-operated brake system or via a hand-operatedexhaust brake or the like. For the sake of clarity, in FIG. 2 first,second and third means are illustrated for determining whether each ofthe three above-mentioned conditions prevail. It will, however, beapparent to the skilled man that since one of the three above-mentionedconditions is always present when a vehicle is moving, it is sufficientto provide means for determining whether any two of the three conditionsare present since the third condition will automatically prevail ifneither of the other two do.

Thus, the system according to the present invention comprises firstmeans 14 for determining whether the engine is driving the vehicle,second means 16 for determining whether the vehicle is braking and thirdmeans 18 for determining whether the vehicle is coasting.

In the first means 14, the CPU is asked at box 20 whether the engine isdriving the vehicle. If the answer is yes, the first means asks at box22 whether the status of any ancillary equipment is below apredetermined minimum level. In the present example, such statuscorresponds to a pressure level in the air tank lower than P_(min). Ifthe status of the ancillary equipment is above the predetermined minimumlevel, then the first means does not switch on the ancillary equipment.This condition is indicated by box 24 in FIG. 2. If, however, the statusof the ancillary equipment is below the predetermined minimum level, thefirst means cause the ancillary equipment to be switched on, asrepresented by box 26. In the present example, the air compressor wouldthus be switched in at box 26 and would continue to operate until apredetermined level of pressure is established in the air tank, whichlevel does not necessarily need to correspond to the maximum levelP_(max).

From the above, it will be apparent that the ancillary equipment is onlyswitched on when the engine is driving the vehicle if the status of anyancillary equipment is below a predetermined minimum level.

Should the first means 14 indicate at box 20 that the engine is notdriving the vehicle, a “no” signal is sent to the second means and thesecond means 16 determine at box 28 whether the vehicle is braking. Ifthe vehicle is found to be braking, the second means ask at box 30whether the status of any ancillary equipment is below a predeterminedmaximum level. In the present example, such status corresponds to apressure level in the air tank lower than P_(max). If the ancillaryequipment has a status corresponding to the predetermined maximum level,the ancillary equipment is not of course switched in. This condition isrepresented by box 32 in FIG. 2. Should, however, the status of theancillary equipment be below the predetermined maximum value, the secondmeans cause the ancillary equipment to be switched on. This condition isrepresented by box 34 in FIG. 2.

Once braking is terminated, it may occur that the status of theancillary equipment is still below the predetermined maximum value. Thisbeing the case, the second means 16 informs the CPU at box 36 of theactual status of the equipment.

Should the second means indicate at box 28 that the vehicle is not beingbraked, then it is apparent that the vehicle must be coasting. Thiscondition is represented by a “no” signal emitted from box 28 enteringthe third means 18.

As previously explained, it is not always desirable to permit ancillaryequipment to be switched on when a vehicle is coasting, since theswitching on of the equipment will cause an increase in engine braking.On the other hand, it is preferable to switch on ancillary equipmentduring coasting rather than when the engine is driving the vehicle.Thus, in accordance with the present invention, a predeterminedintermediate level of the status of the ancillary equipment is stored inthe CPU, this intermediate level being denoted by P_(int) in FIG. 1.Typically, the value of P_(int) may be about 9.5 bar. In a manner whichwill be explained below, the third means are adapted to cause theancillary equipment to be switched on only if the status of theequipment is below this predetermined intermediate level. This impliesthat, in the example of the air compressor, the air compressor would beswitched on if the pressure in the air tank were below P_(int) when thevehicle was coasting.

In the third means 18, it is established at box 38 whether the status ofthe ancillary equipment lies below the predetermined intermediate level.If this is not the case, then the third means commands the CPU 12 towait until the vehicle is braking before switching in the ancillaryequipment. This condition is represented by box 40 in FIG. 2. On theother hand, should the status of the ancillary equipment be below thepredetermined intermediate level, switching on of the ancillaryequipment becomes a possibility.

In a preferred embodiment of the invention, the ancillary equipment isnot automatically switched on as soon as it is determined at box 38 thatthe status of the equipment is below the intermediate level. Instead,the third means 18 may incorporate or communicate with datalogging meansin which parameters relating to operating conditions of the vehicle overa predetermined, immediately preceding, time interval are stored. Thus,at box 42, the third means analyze the parameters relating to theoperating conditions to determine the likelihood of the vehicle beingbraked in the immediate future. If an analysis of the parametersindicates that no braking has taken place for a relatively long time,then it may be deduced that the vehicle is proceeding along a relativelyflat, straight road. Such being the case, the third means causes theancillary equipment to be switched on at box 44 for the period whencoasting is taking place. Of course, the ancillary equipment does notnecessarily have to be kept switched in during coasting until themaximum predetermined level is reached. Instead, an intermediate cutoutlevel lying between P_(int) and P_(max) may be selected.

If after a period of coasting the vehicle is braked, then the ancillaryequipment will continue to be switched on provided its status is belowthe predetermined maximum level.

Conversely, should the coasting phase be followed by an application ofthrottle, the ancillary equipment will be immediately switched out andthe current status of the ancillary equipment noted in the CPU.

If the analysis of parameters represented by box 42 in the dataloggingmeans indicates that a reasonable possibility exists that the vehiclewill be braked in the near future, the third means commands the CPU 12to wait until the vehicle is braking before switching in the ancillaryequipment. This condition is represented by box 40 in FIG. 2.

In a modification of the present invention, the system may be used tocontrol a compressor in an air conditioning unit. Such an airconditioning unit may either be a cab-mounted device or a refrigerationunit for goods carried on the vehicle. In the following, thismodification will be described in relation to a cab-mounted airconditioning device with which the driver selects a suitable temperaturefor the interior of the cab. With reference to FIG. 3, the driverselects a temperature T_(s), for example 21° C. The system according tothe present invention then establishes a maximum temperature T_(max),e.g. 22° C. and a minimum temperature T_(min), e.g. 20° C., to establisha range within which the cabin temperature is allowed to fluctuate. Atemporary maximum value T_(t) is also established, e.g. 23° C. If duringbraking, the temperature in the cab increases above T_(max), thecompressor is switched on to bring the temperature down towards T_(min).Similarly, if during coasting the temperature in the cab is approachingT_(max), the compressor may be switched on. Should, however, thetemperature in the cab exceed T_(max) whilst the engine is driving thevehicle, switching on of the compressor will be delayed in the hope thatthe mode of the vehicle will shortly change over to braking or coasting.Thus, the temperature of the cabin is allowed to reach T_(t) before thecompressor will automatically be switched on.

Naturally, the present invention is not restricted to the embodimentsdescribed above and shown in the drawings, but may instead be variedwithin the scope of the appended claims. For example, in order toprevent ancillary equipment from being switched on when the driver liftshis foot temporarily from the throttle, for example during gearchanging, a delay may be incorporated in the system, for example in thethird means. Furthermore, under certain circumstances, it may bebeneficial to allow the ancillary equipment to be fully charged in onecontinuous cycle. This may occur for example in city driving when thevehicle is frequently accelerating, braking and coasting. In the case inwhich the ancillary equipment includes a cooling fan for assisting inthe cooling of the engine, it will be apparent to the skilled personthat the predetermined minimum level will be a temperature above whichthe fan is automatically switched on, whilst the predetermined maximumlevel will be a temperature below which the fan will not be operated.

What is claimed is:
 1. A system for controlling the switching on ofancillary equipment driven by an engine of a vehicle, said ancillaryequipment being arranged to be driven by said engine until at least aminimum operating level relating to the status of said ancillaryequipment is attained, said system comprising: first means fordetermining whether said engine is driving said vehicle; second meansfor determining whether said vehicle is braking, and third means fordetermining whether said vehicle is coasting, wherein said first meanswill cause said ancillary equipment to be switched on only if the statusof said ancillary equipment is below a predetermined minimum level(P_(min)); said second means will cause said ancillary equipment to beswitched on if the status of said ancillary equipment is below apredetermined maximum level (P_(max)); and said third means will causesaid ancillary equipment to be switched on only if the status of saidancillary equipment is below a predetermined intermediate level(P_(int)) between said maximum level (P_(max)) and said minimum level(P_(min)).
 2. The system as claimed in claim 1, wherein said third meanscommunicates with datalogging means in which parameters relating tooperating conditions of the vehicle over a predetermined, immediatelypreceding, time interval are stored.
 3. A method for controlling theswitching on of ancillary equipment driven by an engine of a vehicle,said ancillary equipment being arranged to be driven by said engineuntil at least a minimum operating level relating to the status of saidancillary equipment is attained, said method comprising: determining inwhich of three modes said vehicle is in, said three modes being a firstmode in which said engine is driving said vehicle, a second mode inwhich said vehicle is being braked and a third mode in which saidvehicle is coasting, and in said first mode causing said ancillaryequipment to be switched on only if the status of said ancillaryequipment is below a predetermined minimum level; in said second modecausing said ancillary equipment to be switched on if the status of saidancillary equipment is below a predetermined maximum level, and in saidthird mode causing said ancillary equipment to be switched on only ifthe status of said ancillary equipment is below a predeterminedintermediate level between said maximum level and said minimum level. 4.The method as claimed in claim 3, wherein when said third mode isentered, account is taken of parameters relating to operating conditionsof the vehicle over a predetermined, immediately preceding, timeinterval before deciding whether said ancillary equipment is to beswitched on.
 5. The system as claimed in claim 1, wherein said ancillaryequipment comprises equipment on the vehicle which requires intermittentcharging or input from the engine.
 6. The system as claimed in claim 1,wherein said ancillary equipment comprises an air compressor for abraking system.
 7. The system as claimed in claim 1, wherein saidancillary equipment comprises a cooling fan for assisting in the coolingof the engine.
 8. The system as claimed in claim 1, wherein saidancillary equipment comprises a servo system for the steering system ofthe vehicle.
 9. The system as claimed in claim 1, wherein said ancillaryequipment comprises an alternator for charging batteries in the vehicle.10. The system as claimed in claim 1, wherein said ancillary equipmentcomprises a compressor for an air-conditioning unit.